FIG. 1 shows a semiconductor light receiving device which is widely used. The reference numeral 1 designates a photo diode. The numeral 2 designates a heatsink. The numeral 3 designates a lead wire. The numeral 4 designates a circular stem on which the heatsink 2 is mounted. The numeral 6 designates a cap. The numeral 7 designates a glass plate window for taking in the incident light. The numeral 8 designates a sealing glass. The numeral 9 designates an electrode. Nitrogen gas is used as the ambient gas 5. It has a dew point that is is low, and it is an inactive gas that has a low cost.
Conventionally, in a mesa-type InGaAs photo diode as an example of the above-described photo diode 1 there is a problem that a yield is low because of a deterioration that occurs at its construction.
On the other hand, a polyimide film has begun to be used as a new surface protection film. FIG. 2 shows a prior art mesa-type InGaAs photo diode which uses a polyimide film. The numerals 14, 13, and 12 designate an n-type InP layer, an n-type InGaAs layer, and a p-type InGaAs layer, respectively, and the numeral 11 designates an electrode. The numeral 15 designates a polyimide film as a surface protection film.
In the semiconductor light receiving device constituted by mounting an InGaAs photo diode with a polyimide film attached to the surface thereof in the package shown in FIG. 1, the incident light 10 from the outside is converted into a current by the photo diode 1, and electrode 9 outputs the converted current.
In the semiconductor light receiving device using a polyimide film, there arises no deterioration at the tie of construction, and a high yield is obtained. Thus it is greatly expected that these devices are put to practical use.
In those devices using a polyimide film, however, the initial value of the dark current is likely to be relatively high, and the dark current is likely to increase as the cumulative amount of time during which the device produces turn-on-electricity, the ON-TIME, increases.
The following is a description concerned with the problem of the dark current:
FIG. 3 shows a dark current vs cumulative ON characteristics at a high test temperature test in the semiconductor light receiving device. The curve A shows the characteristics of the prior art device where the nitrogen gas is sealed after a polyimide film is produced. The curve B shows the characteristics of the prior art device where the nitrogen gas is sealed without producing a polyimide film. As apparent from the curve B, the dark current does not increase in the range of several hundreds of hours of cumulative ON time in the device having no polyimide film. On the contrary, as apparent from the curve A, a rapid increase of the dark current occurs in the above-mentioned range of ON time in the device having a polyimide film.
Another prior art publication, "Polyimide passivation of In.sub.0.53 Ga.sub.0.47 As/InP, and InGaAsP/InP p-n junction structures". by R. Yeats and K. von Dessonneck. Apply. Phys. Lett. 44(1), 1 Jan. 1984, reports that an element having a low dark current is obtained by conducting a passivation to In.sub.0.53 Ga.sub.0.47 As/InP homo-junction photo diode using a polyimide film.